1. Field of the Invention
The present invention relates to a spectroscopic ellipsometer which emits polarized light onto an object to acquire a polarization state of the light reflected on the object.
2. Description of the Background Art
Conventionally, a spectroscopic ellipsometer is installed in a manufacture field for semiconductor devices and used to measure thickness of a film formed on a semiconductor substrate (hereinafter, referred to as “substrate”), optical constants and the like. The spectroscopic ellipsometer emits polarized light onto a substrate to acquire a polarization state at each wavelength of the light reflected on the substrate and performs ellipsometry for some measurements on a single layer film or a multilayer film.
As such a spectroscopic ellipsometer, U.S. Pat. No. 5,910,842 discloses an apparatus which uses only reflection mirrors to guide polarized light from a polarizer to a substrate and guide the light reflected on the substrate to an analyzer, to thereby acquire a polarization state of the reflected light while suppressing occurrence of color aberration.
Recently, since miniaturization and sophistication of circuit pattern on a semiconductor device requires high precision in thickness of a film formed on a substrate, the spectroscopic ellipsometer is required to perform measurements with high accuracy. On the other hand, the spectroscopic ellipsometer is also required to reduce its size for space saving in the manufacture field.
In the method disclosed in U.S. Pat. No. 5,910,842, however, there is a possibility of changing the polarization state of light due to reflectin by the mirrors provided on an optical path between the polarizer and the analyzer or varying the polarization state of light due to some effect of thermal distortion or the like, and therefore it is difficult to acquire change of the polarization state between the light emitted to the substrate and the light reflected thereon (i.e., the polarization state of reflected light) with high accuracy. Though it is possible to suppress the change in polarization state by reducing the incident angle of light to the mirrors, this causes upsizing of the spectroscopic ellipsometer under constraints of construction.